Dry spinning process for preparing coalesced spandex filaments



P. M. SMITH DRY SPINNING PROCESS FOR PREP June 18, 1963 COALESCED SPANDEX FILAMEN Filed July 11, 1961 FIG.

IN V ENTOR PERRY M. SMITH ATTORNEY United States Patent 3,094,374 DRY SHNNING PROCESS FOR PREPARING CQALEEECED SFANDEX FELAMENTS Perry M. Smith, New Shrewshury, N..l., assignor to E. I.

du Pont de Nernours and Company, Wilmington, Del,

a corporation of Delaware Filed Qiuly l1, 1%1, Ser. No. 123,248 3 Cla ms. ((11. 18-54) This invention relates to dry spinning of spandex filaments. More particularly it relates to the production by dry spinning of a coalesced multifilament spandex yarn free of twist.

It is well known that dry-spun spandex filaments are tacky immediately after extrusion. It is also known that bringing a group of such tacky filaments together will produce a coalesced multifilament bundle, which is then usually coated with talc before winding to prevent sticking on the package. Such a coalesced multifilament yarn, which is actually a bundle of tiny individual filaments adhering to one another along their length, is superior in many respects to a single filament spandex yarn of the same denier. For example, in the production of elastic garments the needle of a sewing machine may nick or puncture the elastic yarn. With a monofilament, the nick tends to spread, causing the yarn to break with consequent loss of power and appearance of broken yarn ends in the fabric. A coalesced multifilarnent spandex, on the other hand, resists breakage caused by needle puncture, since breakage of an individual filament does not spread to others in the same bundle.

It is an object of this invention to provide a method for forming a coalesced multifilament having high elasticity and superior interfilament adhesion. Another object is to achieve virtually complete and continuous coalescence of dry-spun spandex filaments. Other objects will appear hereinafter.

These and other objects are accomplished by a process which comprises extruding a solvent-containing solution of a spandex polymer through a spinneret having a plurality of orifices into a spinning cell to form a plurality of separate filaments. An evaporative medium such as a heated gas is simultaneously introduced into the cell to evaporate the solvent from the solvent-containing filaments. The filaments are withdrawn from the cell through an outlet, passed through a vortex of circulating gaseous fluid, and then passed in contact with the surface of a forwarding roll. The circulating gaseous fluid exerts a torque on the filaments, thereby imparting a false twist which extends from the forwarding roll back along the line of the filaments into the spinning cell. The false twist must extend back into the cell to a point at which the filaments are in a sufiiciently plasticized state to adhere to each other, thereby forming a false-twisted, coalesced multifilament. The twisted multifilament is passed in contact with the forwarding roll under sufficient tension to counteract the torque imparted by the circulating fluid, thereby removing the false twist and permitting the coalesced multifilament to be wound up essentially free of twist. As a general rule, the false twist extends for a considerable distance into the spinning cell, preferably for at least 25 of the distance of travel of the filaments through the heated portion of the spinning cell.

By the process of the present invention, the spinning and coalescing steps can be carried out in such a manner that the spandex filaments do not come in contact with any solid surface from the time they are formed in the spinning cell until the time they are forwarded as an untwisted, coalesced multifilament to a collecting device.

In practicing the present invention, the false twist is imparted by passing the filaments through a jet twister at a position between the spinning cell and the forwarding means. The jet twister, which will be more fully described later herein, has an aperture for receiving the filaments and an annular plenum chamber surrounding the aperture into which a gaseous fluid is introduced tangentially, thereby providing a lubricating layer of centrifugally circulating fluid about the filaments. The circulating fluid exerts a torque on the filaments as previously described. By usual manipulation of spinning conditions for dry spinning spandex polymer and by properly controlling the pressure of the gas introduced into the jet twister, the jet functions both as an air-lubricating yarn guide as well as a false twister for coalescing the filaments.

One embodiment of the invention is shown by way of example in the accompanying drawing wherein:

FIGURE 1 illustrates, in diagrammatic fashion, spinning apparatus arranged to carry out the invention;

FIGURE 2 is a View of the top of a jet twister suitable for use in the practice of the invention; and

FIGURE 3 is a sectional view of the jet twister taken along the line 3-3 of FIGURE 2.

in the dry spinning of spandex filaments, a solution of the segmented polyurethane is first prepared, preferably by carrying out the polymerization in the solvent to be used for the spinning operation. The spinning solution of suitable viscosity is pumped to a spinneret assembly 10 mounted in the dry spinning cell 12. As the solution is extruded from the spinneret, it is met by a co-current stream of hot, inert gas introduced to the cell through inlet 14. The solvent of the spinning solution is evaporated into the hot, inert gas, thereby converting the several streams of spinning solution into continuous filaments 16 as they proceed down the cell. A countercurrent stream of inert gas may also \be introduced at the bottom of the cell through inlet 18 to minimize dripping of solvent from the cell. The two streams of inert gas meet and are drawn off through an aspiration device 20 near the bottom of the cell. The solvent may be recovered from the drawn-off gas for reuse in the preparation of additional spinning solution.

The filament bundle exits through a small hole 30= in the cell closure and passes through the jet twister 22 to the feed roll 28. The hole in the cell closure and the jet twister are positioned with respect to the feed roll 28 such that the filaments pass from the spinneret to the feed roll without touching the cell closure or the walls of the jet. Thus, the only contact with a solid surface that the yarn would have prior to reaching roll 28 is an occasional or accidental contact with the wall of the jet or the hole in the cell outlet.

The jet twister 22 is supplied with a steady flow of air through inlet 24. The action of the jet is such as to twist the filament bundle 26 passing through it. The fiow of air to the jet is adjusted so that this twist backs up into the cell to a point 27, which is the first point of filament-tofilament contact.

Since the twist applied is false tvn'st, the coalesced multifilament leaves roll 28 essentially free of twist. It then passes over a finish roll 32 for application of a lubricant from reservoir 33, thence to a second feed roll 34, and thence to a wind-up apparatus consisting of a traversing yarn guide 36, a drive roll 38, and is wound up on bobbin 4% Roll 34 may be operated at a slightly lower, equal, or slightly higher linear speed than roll 28, depending upon the denier, spinning speed, and spinstretch ratio desired. The relative speed of these rolls is adjusted to overcome friction encountered while finish is being applied at roll 32. The multifilament may be partially or completely relaxed between roll 34 and roll 38 to give the desired winding tension in the packaged yarn and to develop desirable physical properties in the final product.

The jet twister 22 consists essentially of a doughnutshaped plenum chamber supplied with a tangential air inlet 24. The yarn passes through orifice 23 located at the center of the doughnut and is twisted by a swirling sheet of air issuing perpendicularly to the thread line from orifice 25. The diameter of the orifice 23 may range from 0.025 inch to 0.5 inch and higher and the length of this orifice may range from approximately 0.3 inch to 1 inch. A

low ratio of length to width for this passageway is de-' sirable. The orifice 25 is made as narrow as possible, of the order of of an inch.

Best results are obtained with jets having the following characteristics: First, the central orifice 2:3 is made as small as practicable to reduce lateral movement of the threadline. Secondly, a very thin, continuous sheet of air issues from orifice 25 completely around the filament bundle. This feature gives added stability to the threa line. Thirdly, orifice 23 is made as short as possible to minimize the area of possible contact with the filaments and thereby reduce plucking, which causes variations in the tension of the packaged product. The jet twister may be hinged at one side (not shown), so that it may be opened for string-up purposes. This feature allows the air passages to be readily inspected and cleaned without removing the device from the spinning machine.

' This invention i further illustrated but is not intended to be limited by the following example in which parts and percentages are by weight.

Example Into a reverse centrifugal mixer maintained at 50 C. are fed a stream of polytetramethylene ether glycol at a rate of 8 pounds per hour and a stream of liquid p,pmethylenediphenyl diisocyanate at 2 pounds per hour. The polytetramethylene ether glycol has a molecular weight of about 2000 and is thoroughly pro-dried by treatment with a molecular sieve. The reagents are intimately mixed, remain in the mixer for one minute, and are discharged continuously into a jacketed pipeline maintained at about 96 C. and extending for 25 feet. The pipeline serves as a reactor in which the polyether glycol is capped with 2 mols of the diisocyanate to yield an isocyanate-terminated polyether. The average time spent in the reactor is between 90 and 100 minutes. On emerging from the pipeline reactor, the isocyanate-terminated polyether is cooled at once to below 45 C. The cooled isocyanate-terminated polyether is conducted at a rate of 9.2 pounds per hour into a high-shear mixer containing a rotating disc, and a stream of N,N-dimethylformamide is added at 42.8 pounds per hour. The mixture (17.7% solids) is thoroughly agitated for 4 minutes and then passes to a chamber in which a mixture of hydrazine (35% in water) and diethylamine (5% in dimethylformamide) in the ratio of 37.5 parts of hydrazine to 1 part of diethylamine is added as a single stream at a rate of 0.465 pound per hour with strong agitation. The mixture passes to a reaction chamber held at a temperature of 20-40" C., the contents having a residence time of about 2-3 minutes. The emerging polymer solution contains approximately 17.7% solids and has a viscosity of 700 poises at 30 C. The polymer has an inherent viscosity of 1.5. To the polymer solution are added a slurry of titanium dioxide in dimethylformamide and a solution of poly-(N,N-diethyl beta-aminoethyl methacrylate) in dimethylformamide such that the final mixture contains 5% of each additive based on the elastomeric solids.

The foregoing mixture is heated to a temperature of 70 C. and extruded through a spinneret containing 43 holes into a spinning column 20 feet in length. Kemp gas, essentially a mixture of about 87% nitrogen and 13% carbon dioxide, heated to 340 C. is introduced at the top of the spinning column and is drawn off at a point about 4 feet above the exit point of the filament bundle. Below the column, the filaments pass through a jet twister having a circular air slot 0.017 inch in width and a yarn orifice 0.063 inch in diameter and 0.875 inch in length. Air is supplied to the jet at the rate of 20 spasms cubic feet per hour. Twist in the filament bundle is backed up from the jet into the column to a point about 9 feet above the exit point of the bundle, i.e. slightly more than 30% of the path of travel of the filaments through the heated portion of the spinning column. The well coalesced multifilarnent of about 280 denier leaving the jet is passed over a roll turning at a linear speed of 535 yards per minute, is treated with an oil-based finish, is passed over another roll turning at 535 yards per minute and is wound up at 532 yards per minute.

The segmented polyurethanes from which the spandex filaments are obtained are generally prepared from hydroxyl-terminated prepolymens, such as hydroxyl-termihated polyethers and polyesters of low molecular Weight. Reaction of the prepolymer with a molar excess of organic diisocyanate, preferably an aromatic diisocyanate, produces 'an isocyana-te-terminated material which may then be chain-extended with a difunctional, active-hydrogen containing compound, such as water, hydrazine, organic diamines, glycols, aminoalcohols, etc. Many segmented polyurethanes of this type are described in several patents and are useful in the practice of this invention. Among these are US. Patents 2,929,800, 2,929,801, 2,929, 802, 2,929,804, 2,957,852, 2,962,470, 2,965,437, and U5. Re. 24,689. These patents teach that elastic filaments may be made from segmented polyurethanes which contain seg ments of a high-melting, crystalline polymer alternating in the chain with segments of a low-melting, amorphous polymer. The crystalline, high-melting segment may be derived from, for example, a polyurea, polyurethane, polyamidc, or bis-ureylene polymer. The low-melting, amorphous segment may be derived from, for example, a polyester, a polyether, or an N-alkylated polyurethane. As taught by the aforementioned patents, many of the segmented polyurethanes when in filament form display elongations at the break in excess of 200%, elastic recovery (or tensile recovery) of above about 90%, and stress decay of below about 20%.

As indicated hereinbefore, the segmented polyurethanes are preferably prepared by carrying out the polymerization reaction in the solvent to be used for spinning. Conventional procedures may be used for preparing such polymer solutions. Solvents which have been found satisfactory for use in the dry spinning operation include N,N-

dimcthylformamide, N,N-dimethylacetamide, tetramethylenesulfone, formic acid, and mixtures of 1,1,2 trichloroethane with formic acid. The spinning solution may contain from 15% to 30% or more of polymer solids depending on solution viscosity and may be preheated prior to introduction to the spinneret. Viscositieis of the order of 400 to 1000 poises are conveniently handled. The inherent viscosity of the polymer should be above 0.6, prefenably above 1.0.

The backing up of twist from the jet twister into the spinning cell has the effect of reducing the total filament area from which solvent may be evaporated. A balance must thus be struck between acceptable coalescence and adequate solvent removal. Depending on the denier of the spandex yarn being processed, the temperature and gas flow rate within the spinning cell, and the particular design of jet twister, air to the twister may be supplied at how rates from about 10 lllO about 25 cubic feet per hour. The point 27 to which the twist extends back in the cell and at which the plurality of filaments converge is controlled in the present process by adjusting the air fiow rate. Preferably, this point is as close to the ispinneret as possible and still permit reduction of the solvent content to less than about 2% by weight of the emerging filaments. The heated portion of the cell extends from hot gas inlet 14 to the point of attachment of aspiration device 20. The distance from 2'7 to 20 should generally be adjusted to exceed 30% of the heated portion of the cell. It is, of course, understood that in addition to the use of heated inert gas, the cell walls may be heated and that such heating may be done with vapor, with liquid, or electrically.

By the process of this invention, spandex multifilaments of from about 40 to 840 denier and above may be obtained by coalescing varying numbers of individual filaments. The individual filaments may be from about 2 to about 20 denier per filament.

Multiple-thread spinning may be accomplished using the present invention by gathering the filaments issuing from the spinneret into separate groups, e.g. four, and conducting each group of filaments to a separate air jet twister located beneath the cell. This modification is obviously useful when not all of the filaments issuing from a single spinnereit are needed to make up the final coalesced multifiiament. When multiple-thread spinning is practiced, it is advantageous to use a mult-i-stream pump, e.g. a four-stream pump, to supply lspinning solution to the separate groups of orifices in a spinneret.

After leaving the air jet twister and roll 28, the coalesced multifilament is usually coated with a finish to elimate yarn tackiness and permit winding the coalesced multifilament onto a package from which it can be unwound without tension plucks. The finish may consist of a suspension of tale in aqueous acetone. Alternatively, various oil-based finishes may be used, as described in copending application S.N. 18,264, now Patent No. 3,039,- 897. An aqueous finish usually requires that the yarn be dried for some period of time before use, whereas an oilbased finish requires no such treatment and furthermore, eliminates the abrasive effect of a talc-finished product.

A package of more uniform tension is obtained if a matte finish is applied to both rolls 28 and 32. Preferably, the arc of contact of the threadline against roll 32 is made as low as possible, e.g. less than The coalesced multifilament is shown in FIGURE 1 as being wound directly on the final bobbin 40. 'It is to be undenstood that various after-treatments may be performed on the product before final windup. A multifilament spandex may be drawn and repackaged as a different denier, and the drawing process may be combined with the spinning wind-up process. If desired, several coalesced multifilaments taken either directly from the spinning machine or from wound packages may be made into a multiend tape.

The process of the present invention has the advantage that coalescence of the individual filaments occurs in a dry, uncontaminated space immediately after extrusion, thereby insuring maximum interfilament adhesion. This results, of course, because the false twist device is located well below the point of initial filament-to-filament contact. The method of this invention offers a distinct advantage over other coalescence methods, particularly in cases where multiple-thread spinning is desired. The compact size of the jet twister permits locating several jets below the ordinary spinning cell.

The filaments of this invention find particular utility in foundation garments, girdles, corsets, surgical hosiery, woven or knitted swim wear, socks and sock tops. The filaments are also useful in brassieres, suspenders, garters, slip tops, lingerie straps for slips and brassieres, form fitting hosiery afterwelts, support hosiery, surgical bandages and tapes, medical supports, panties, waistbands, leg bands, wristlets and jacket trim, dresswear, rainwear, skirts, sweaters, belts, suits, coats, hats, slacks, pajamas, skin diving suits, leotards, athletic uniforms, polo shirts, ski clothing, golf jackets, golf balls, golf club mittens, gloves, sling shots, watch straps, narrow tapes and webbings, braids, sewing thread, shoelaces, hairnets, chin straps, shoe gores, shoe fabrics, carpets and rugs, furniture upholstery, slip covers, automobile upholstery, mattress covers, fitted sheets and bedding, ticking and quilting fabric, laundry bags, card table covers, shock cord core, industrial belting, wire and cable jackets, anti-gravity suits, crash barriers, wall covering, toupee bases, face masks, woven and nonwoven fabrics, felts, papers, book covers and jackets, coatings, protective coverings, swimming pool covers, flannels, and protective clothing.

The filaments of this invention may be blended with relatively nonelastic filaments, e.g., nylon and/or nonelastic filaments in the stretchy form for making a wide variety of elastid or stretchy products including woven, knitted and nonwoven fabrics for use in universal fitting apparel, e.g., socks, stockings, elastic cuffs, action sportswear, and others as listed hereinbefore; household products, e.g., form-fitting upholstery; industrial products, e.g., woven and nonwoven felts, resilient pads and films, synthetic leather, filter fabrics, stuffing material, boat covers, balloon fabrics, sleeping bags, hammocks, automobile tops, and tarpaulins; and medical products, e.g., surgical stockings and splint tapes. The filaments of this invention can be employed in the aforementioned applications in the form of either continuous filaments or as a blend of staple fibers, as appropriate.

As many widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that this invention is not to be limited to the specific embodiments thereof except as defined in the appended claims.

I claim:

1. A process for preparing a coalesced multifilament which comprises extruding a solvent-containing solution of a spandex polymer through a spinneret having a plurality of orifices therein into a spinning cell to form a plurality of separate filaments, forwarding said filaments in an unsupported fashion through said cell while simultaneously introducing into said cell a gaseous evaporative medium, Withdrawing said filaments from said cell through an outlet remote from said orifices and thence through a vortex of circulating gaseous fluid wherein said fluid exerts a torque on said filaments imparting a false twist thereto, said false twist extending back along the line of said filaments into said cell to a point at which the filaments are in a sufficient plasticized state to adhere to each other thereby forming a false-twisted coalesced multifilament, passing said twisted multifilaments from said vortex into contact with forwarding means under suflicient tension to counteract said torque imparted by said vortex thereby removing said false twist.

2. The process of claim 1 wherein said false twist is imparted by a jet twister having an aperture for receiving said filaments and an annular plenum chamber surrounding said aperture into which a gaseous fluid is introduced tangentially to provide a lubricating layer of circulating fluid about said filaments.

3. In a dry spinning process for preparing coalesced spandex filaments which comprises extruding a solventcontaining solution of spandex polymer through a plurality of orifices into a spinning cell containing an evaporative medium and withdrawing said filaments from said spinning cell by passing them in contact with forwarding means remotely positioned from said spinning cell, said filaments being unsupported between said orifices and said forwarding means, the improvement which comprises imparting a false twist to said filaments to form a coalesced multifilament by passing said filaments through a jet twister at a position between said spinning cell and said forwarding means, said jet twister having an aperture for receiving said filaments and an annular plenum chamber surrounding said aperture into which a gaseous fluid is introduced tangentially to provide a lubricating layer of circulating fluid about said filaments, said fluid exerting a torque on said filaments thereby imparting a false twist thereto which extends along the unsupported length of said filaments from said forwarding means into said cell to a point at which said filaments are in a sufficiently plasticized state to adhere to each other, said twisted filaments being passed in contact with said forwarding means under sufficient tension to counteract said torque imparted by said fluid layer thereby removing said false twist.

References Cited in the file of this patent UNITED STATES PATENTS 2,352,861 Pierce July 4, 1944 

1. A PROCESS FOR PREPARING A COALESCED MULTIFILAMENT WHICH COMPRISES EXTRUDING A SOLVENT-CONTAINING SOLUTION OF A SPANDEX POLYMER THROUGH A SPINNERET HAVING A PLURALITY OF ORIFICES THEREIN INTO A SPINNING CELL TO FORM A PLURALITY OF SEPARATE FILAMENTS, FORWARDING SAID FILAMENTS IN AN UNSUPPORTED FASHION THROUGH SAID CELL WHILE SIMULTANEOUSLY INTRODUCING INTO SAID CELL A GASEOUS EVAPORATIVE MEDIUM, WITHDRAWING SAID FILAMENTS FROM SAID CELL THROUGH AN OUTLET REMOTE FROM SAID ORIFICES AND THENCE THROUGH A 